Servo steering system

Abstract

An electrically energized power steering system for vehicles is disclosed using a clutch that disengages the servomotor at times of near zero driver input torque. The servomotor is energized for power assist in executing turns and for synchronizing servomotor speed with the steering mechanism during the return of the dirigible wheels to the straight ahead position and at other times when the clutch is disengaging the servomotor thereby eliminating clashing upon clutch reengagement. A torque transducer operatively coupled with the steering wheel shaft and the steering gear generates a torque signal corresponding to the torque applied by the driver to the steering wheel. Two tachometers are provided, one on the servomotor and one on the steering wheel shaft and the outputs are combined to develop a signal corresponding to differential speed. The torque signal and the differential speed signal are added and the resultant signal is applied to the servo amplifier which energizes the servomotor. When the driver turns the steering wheel the clutch engages the servomotor, the torque signal predominates and the servomotor is energized to provide power assist. When the driver releases the steering wheel, the torque signal drops to approximately zero and the differential speed signal controls the energization of the servomotor to maintain its speed in near synchronization with the return of the dirigible wheels to the straight ahead position.

What is claimed is: 
     
       1. In a vehicle power steering system of the type comprising a manual input means, a steering gear, an electric servomotor having an output shaft, a clutch operatively disposed between said output shaft and said steering gear and adapted to be engaged or disengaged, means for generating a torque signal corresponding to the torque transmitted by said manual input means, and control means adapted to control the energization of said servomotor in accordance with said torque signal, the improvement comprising: synchronizing means for controlling the energization of said servomotor for rotation of said output shaft in approximate synchronization with the rotation of said manual input means when said clutch is disengaged.   
     
     
       2. The invention as defined in claim 1 wherein said synchronizing means comprises: a first tachometer adapted to produce a first tachometer signal corresponding to the rate of rotation of said manual input means,   a second tachometer adapted to produce a second tachometer signal corresponding to the rate of rotation of said output shaft of said servomotor,   means responsive to said tachometer signals for producing a difference signal,   means responsive to said difference signal for controlling the energization of said servomotor.   
     
     
       3. The invention as defined in claim 2 wherein said means responsive to said difference signal comprises: means for combining said difference signal with said torque signal for developing a control signal,   an amplifier,   and means for applying said control signal to said amplifier for controlling the energization of said servomotor.   
     
     
       4. The invention as defined in claim 1 wherein, said means for generating a torque signal comprises an angular motion to linear motion converter with a means for converting linear motion to an electric signal.   
     
     
       5. In a vehicle power steering system of the type comprising a manual input means, a steering gear, an electric servomotor having an output shaft, a clutch operatively disposed between said output shaft and said steering gear and adapted to be engaged or disengaged, means for generating a torque signal corresponding to the torque transmitted by said manual input means, and control means adapted to control the energization of said servomotor in accordance with said torque signal, the improvement comprising: a first tachometer adapted to produce a first tachometer signal corresponding to the rate of rotation of said manual input means,   a second tachometer adapted to produce a second tachometer signal corresponding to the rate of rotation of said output shaft of said servomotor,   means responsive to said tachometer signals for producing a difference signal,   means responsive to said difference signal for controlling the energization of said servomotor.   
     
     
       6. The invention as defined in claim 5 including speed reducing gear means operatively coupled between said servomotor and said steering gear wherein said difference signal varies directly with the difference between the rotational speed of said manual input means and the rotational speed of said servomotor output shaft reduced by the reduction ratio of said speed reducing means. 
     
     
       7. The invention as defined in claim 6 wherein, said speed reducing gear means comprises a planetary reduction gear means.   
     
     
       8. The invention as defined in claim 5 wherein said means responsive to said difference signal comprises: means for combining said difference signal with said torque signal for developing a control signal,   an amplifier,   and means for applying said control signal to said ampifier for controlling the energization of said servomotor.   
     
     
       9. The invention as defined in claim 5 wherein, said means for generating a torque signal comprises an angular motion to linear motion converter with a means for converting linear motion to an electric signal.